2013/04/17 Council Agenda Packet

1 Partial Separation Concept Partial separation involves reducing the amount of surface water runoff that enters the combined sewer system but not completely eliminating it.Two approaches will be analyzed.The approach will evaluate keeping low flows in the combined sewer system so that stormwater treatment is provided at the wastewater treatment plant.Flows greater than what are required for treatment would be diverted through a flow splitter and discharged directly to the Snohomish River. Consultant will perform hydraulic analysis,and assess the feasibility of additional potential stormwater separation areas west of I-5 that could discharge to systems within the East Grand Area. Consultant will develop conceptual construction cost estimates and summarize the evaluation and alternatives in a design memorandum. Consultant will periodically meet with City staff throughout the evaluation/analysis to discuss findings and obtain feedback and additional direction relative to stormwater separation options. Consultant will meet and discuss strategies on the City's desire to prepare application for grant • funding of the proposed stormwater separation project.Consultant will assist by reviewing,advising, and providing narrative write-ups and/or data to assist the city in their preparation and submittal of the grant application. I.2 Supplemental Surveying and Basemapping The previous survey/base mapping primarily followed the alignments of the existing sewer proposed for replacement(approximately 9,500 lineal feet of street/alleys). Consultant will field survey and supplement the basemaps for the additional areas proposed for sewer replacement and additional areas proposed for separate underground storm sewer system(approximately 13,500 lineal feet of additional street/alleys,collectively). Consultant will retain a locate service to mark underground utilities and field surveyed and mapped utilities based on surface markings and record as-built drawings.Additional survey limit are generally described as follows: • Supplemental E.Grand Avenue—23rd Street to 20th Street. • Cleveland Avenue-Everett Avenue to termini at I-5. • Supplemental Harrison Avenue—LS#32 to California Street to Everett Avenue;and 25th Street to 21St Street. • Supplemental Summit Avenue—Alley north of Everett Avenue to 25th Street. • 20th Street-Alley Way to East Grand Avenue. • 215`,22nd,23'd,24th,and 25th Streets—each between Harrison Avenue and East Grand Avenue. • 26th Street—Summit Avenue to East Grand Avenue. • Supplemental Everett Avenue—Highland Avenue to Summit Avenue. • California Street—Highland Avenue to Harrison Avenue. Sewer System Replacement and Capacity Improvements Project 7 otak K\project\31500\31520\Contract\Amend4\AmendFour\AmendmentFoux021413.docx 8